Currently, the majority of autonomous and mobile electronic systems are powered by electrochemical batteries. Although the battery quality has substantially improved over the last two decades, their energy density has not greatly increased. At present, factors such as cost, weight. limited service time and waste disposal problems (intrinsic to batteries) are impeding the advance in many areas of electronics. The problem is particularly acute in the portable electronics market, where rapidly growing performance and sophistication of mobile electronic devices has led to ever-increasing power demands that traditional electrochemical batteries are unable to meet.
One of the technologies that holds great promise to substantially alleviate the current reliance on the electrochemical batteries is high power energy harvesting. The concept of energy harvesting works towards developing self-powered devices that do not require replaceable power supplies. In cases where high mobility and high power output is required, harvesters that convert mechanical energy into electrical energy are particularly promising, inasmuch as they can tap into a variety of “high power density” energy sources that exhibit mechanical vibrations.
High power harvesting of mechanical energy is a long-recognized concept, yet it has not been able to be commercialized, due at least in part to the lack of a viable energy harvesting technology. Existing methods of mechanical-to-electrical energy conversion such as electromagnetic, piezoelectric, or electrostatic do not allow for effective direct coupling to most of the high power environmental mechanical energy sources. Bulky and expensive mechanical or hydraulic transducers are required to convert a broad range of aperiodic forces and displacements typically encountered in nature into a form accessible for conversion using these methods.
Recently, a new approach to energy harvesting has been proposed that substantially alleviates the above-mentioned problems, the new approach being the use of a micro fluidics-based energy harvester. In particular, a high power microfluidics-based energy harvester is disclosed in U.S. Pat. No. 7,898,096 entitled “Method and Apparatus for Energy Harvesting Using Micro fluidics” issued to T. N. Krupenkin on Mar. 2, 2011 and herein incorporated by reference. The Krupenkin energy harvester generates electrical energy through the interaction of thousands of microscopic liquid droplets with a network of thin-film electrodes. A typical configuration of the Krupenkin energy harvester is capable of generating several watts of power. An exemplary embodiment of this Krupenkin energy harvester is shown in FIG. 1, which illustrates a train of energy-producing conductive droplets 1 located along a microscopically thin channel 2, where droplets 1 are suspended within a liquid dielectric medium 3 and are hydraulically actuated by applying a pressure differential between the ends of channel 2. Pluralities of separate electrodes 5-1 and 5-2 are disposed along either side of channel 2, which engage with droplets 1 as they move back and forth within channel 2 during changes in pressure. As conductive droplets 1 move along channel 2, they create arrays of capacitors with electrodes 5-1 and 5-2, the capacitors changing in stored charge as the droplets move back and worth, generating an electrical current flow. This type of hydraulic activation method provides an important advantage as it allows for efficient direct coupling with a wide range of high power environmental mechanical energy sources, including human locomotion.
While the microfluidic-based energy harvester as shown in FIG. 1 exhibits a significant improvement over the state of the art, this actuation method is not well-suited for applications where the energy is being harvested from mechanical vibrations, since the displacement amplitude of a vibration is often too small to initiate motion of droplets along a channel. Yet, such vibrations constitute a readily available source of energy in many important environments, including transportation (e.g., automotive, aerospace, rail), industrial machinery, and the like. Thus, any method that can provide effective actuation of microscopically small liquid droplets by environmental mechanical vibrations would be highly beneficial, as it would allow for the extension of energy harvesting to a broader range of environments.